1. Field of the Invention
This invention relates generally to transmissions for tracked vehicles such as military tanks and more specifically to transmissions which include a hydrodynamic converter, a main shaft arranged on an axis transverse to the converter and a steering unit wherein the transmission components are arranged in a novel space and weight saving configuration.
2. Brief Description of the Prior Art
Transmission systems for tracked vehicles have employed torque converters for driving transversely oriented main shafts. Additionally included as part of such transmissions were reversing gears, main shaft speed change gears and a steering drive which engaged planetary differential gears through a zero or neutral shaft.
Typical examples of such prior transmission systems were described in United Kingdom Pat. No. 1,526,542 entitled "Gear Box for Controlling Endless Track Vehicles" and in German Pat. No. 1,655,915, both issued to the assignee of the present invention.
Among the disadvantages of such transmission systems have been the prior design of the gearing arrangements and component placement which resulted in extended distances between the torque converter and the transmission output shaft. One of the reasons for such prior configurations was that bevel gear assemblies and other equipment such as steering drives were often positioned between the torque converter and the transmission main shaft. The size of the transmission systems were of course critical in the design of the tracked vehicle itself and affected vehicle weight, engine space, engine power requirements and total vehicle cost.
In one attempt at reducing the space requirements of such transmission systems, the torque converter was positioned along an axis parallel or coincident with rather than transverse to the main shaft. This approach suffered significant drawbacks, however, because the engine output shaft was transverse to the converter input shaft. As a result, power transfer gear trains were required between the engine and the converter.
These gear trains were subject to substantial vibration stress, especially in vehicles driven by reciprocating piston engines. Because of the stresses involved, the gears were required to be massive. As a result, the weight and cost of the transmission increased. Alternatively or conjunctively with the heavy mass gear trains, additional vibration isolation devices such as vibration damping couplings were required. As a result, space, weight and cost reduction were not attainable with this prior approach.
Other problems which have been encountered with prior tracked vehicle transmission systems included difficulties in assembly and servicing which have been due to the fact that component subassemblies have not generally been constructed as units capable of easy independent initial installation or subsequent replacement.
In United Kingdom Pat. No. 1,526,542, a recognition of this problem was demonstrated and transmission subassemblies which could be replaced without substantial transmission dismantling were disclosed. These subassemblies were accessed through removable covers in the transmission casing. Even with the structure suggested in this patent, the replacement of subassemblies was still cumbersome, components within the casing were still difficult to reach and the installation of replacement units including alignment and mounting remained a formidable task.
The present invention deals with a further problem which has been encountered with braking systems of prior tracked vehicle transmission systems. Flow brakes have been employed as an adjunct to the main braking system of the vehicle which usually included disc brakes. In the past, the flow brake was driven by the transmission main shaft. The effectiveness of such flow brakes decreased with shaft speed, however, and little or no braking effect was achieved when the vehicle was driven slowly. As a result, relatively large, heavy and costly flow brakes were required.